Adams Arms is sort of a grab bag of reliability. The overall operation of them is generally fine, but you have secondary problems that arise. The Adams Arms system is basically a plug-n-play system, which is designed to work with any AR system. This level of easy integration makes the kits very simple to install, and relatively inexpensive. So much so that other companies like Huldra use AA kits for their own rifles. I would much rather recommend a fully-built upper than a kit conversion, as you will know that the system was installed absolutely correctly (or would be warrantied to be so). Then, you just have to deal with the ancillary problems that pop-up. The major issues are with carrier tilt and the related wear issues, return spring fatigue and gas regulation issues.
Piston guns in general are harder to diagnose when they have problems, but that's across the whole board.

LWRC is a great company and they have excellent products that a lot of big name people like Jeff Gonzalez promote. As long as you replace the piston return spring every 3000 rounds, it'll keep running strong.